The secondary lining is not considered as a load-bearing structure in tunnel design. However, the current field measurements of tunnels show that the secondary lining is subjected to some load. Therefore, it is necessary to study the load sharing ratio of the secondary lining in detail. This paper analyzes the load sharing ratio of the secondary lining based on the thick-walled cylinder theory. Based on this theory, an observational design method and process for soft rock high-deformation tunnels are proposed, which integrate field measurements and consider the construction duration, facilitating design and construction. Additionally, the contact pressures between the surrounding rock, the initial support, and the secondary lining, were statistically analyzed for more than 60 tunnels. The statistical analysis shows that the worse the surrounding rock, the higher the contact pressure between the surrounding rock, the initial support, and the secondary lining. Finally, combining the field measurements of the Jingzhai tunnel and the thick-walled cylinder theory, the contact pressure of the secondary lining was determined to be 6110 kPa in the observational design, which is very close to the subsequent measured value of 6690 kPa, validating the effectiveness and accuracy of the proposed observational design method. The results of this paper provide reliable theoretical references and empirical guidance for the design and construction of tunnels.